1. Field of the Invention
The present invention relates to a saddle-riding type vehicle having a power unit which incorporates an electric power transmission apparatus.
2. Description of Background Art
Heretofore, a transmission mechanism for actuating a transmission in a motorcycle is known wherein an electric power transmission apparatus for changing gears is provided with an electric motor. See, for example, Japanese Patent Laid-Open No. 2010-196855. The transmission mechanism includes the electric motor as a gearshift motor for supplying power to change the gears of the transmission, a gear set as a speed reducer gear mechanism for reducing the rotational speed of the electric motor, and a screw as a change mechanism for angularly moving a shift drum through a prescribed angle to change the gears.
More specifically, a longitudinally oriented internal combustion engine includes a crankshaft extending along the longitudinal direction of the vehicle and the transmission that is integrally combined with the crankshaft to make up a power unit. The screw that actuates the transmission is disposed in a front portion of the power unit with the electric motor that supplies rotational power to the screw being disposed in front of a transmission case for housing the transmission and immediately behind the front wheel of the vehicle. With this structure, the change mechanism including the screw, etc. and the electric motor are disposed close to the front portion of the power unit, making it possible to render the electric power transmission apparatus compact.
According to the structure disclosed in Japanese Patent Laid-Open No. 2010-196855, the power unit is shaped such that in a side view of the vehicle, the front face of an upper portion of the power unit wherein the internal combustion engine is disposed projects more than the front face of a lower portion thereof wherein the transmission is disposed, providing a cavity in front of the lower portion of the power unit. The shift motor is placed in the cavity, with a clearance defined between the front wheel and the shift motor. Therefore, when the vehicle is suddenly braked, the front wheel and the shift motor are prevented from contacting each other, and pebbles which may come flying from the front wheel are less likely to hit the shift motor.
However, depending on the internal structures and layout of the internal combustion engine and the transmission, it is difficult in some instances to provide the cavity in front face of the power unit. According to the layout of a conventional electric power transmission apparatus, if attempts are made to render the electric power transmission apparatus compact by clustering the shift motor and the change mechanism in a forward direction of the power unit, then it is difficult to define the clearance between the front wheel and the shift motor.